1. Field of the Invention
This invention pertains to composite poles, such as utility poles, light poles and antennas having an integral foam core and methods of making and using them.
2. Description of the Prior Art
There is a substantial prior art with respect to composite poles such as utility power transmission poles, light poles, and the like, and methods of making them. Composite poles refers to the fact that the poles are formed from a combination of different materials each of which maintains their identities in the combination to produce a superior result than could be achieved from the individual materials. The composite for making poles is generally fiber-reinforced plastic (FRP), typically fiberglass fibers in a resin matrix, producing what is generally called a fiberglass pole. The reinforcing fibers are not limited to fiberglass, however, and can include the likes of asbestos, jute, sisal, aramid fibers, carbon fibers, and synthetic fibers, though fiberglass has typically been associated with large poles. Resin refers to any polymer that is the matrix for a composite, such as epoxies, polyesters, acrylics and other polymers. The major requirement is that the reinforcing material forms a strong bond to the resin.
The processes for making fiberglass poles involves forming a hollow tube while the resin is in a plastic state and then curing the resin. Curing refers to the process of converting the resin from a plastic state to a hardened state by application of heat, catalyst, ultra-violet light or reactants (curing agents) which convert the resin into a hardened structure, generally three dimensional cross linked structure, which is insoluble and will decompose before it melts.
There are two principal classes of processes known in the prior art for making composite, principally fiberglass poles. These are known as filament winding and pultrusion. A third alternative is a hybrid of filament winding and pultrusion.
Filament winding refers to a process for making an FRP in which a continuous filament or tape is treated with resin and wound onto a mandrel (a metal form whose outer shape is the same size as the desired inner surface of a pole under construction) in a predetermined pattern. The process is performed by drawing the filament from a spool or creel (a creel is a spool and supporting structure) through a bath of resin, then winding it onto the mandrel under controlled tension and in a predetermined pattern. The mandrel may be stationary, in which case the creel structure rotates above the mandrel, or it may be rotated on a lathe about one or more axes. After a sufficient number of layers have been wound the resin is cured and the hardened hollow pole is removed from the mandrel.
U.S. Pat. No. 4,089,727 to Hardy—The McLain, which is hereby incorporated herein in its entirety by reference, disclosed an apparatus and method for preparing a member by wrapping a mandrel with discrete layers of fiber by applying filaments in expanded helices while selectively varying the lead angle of helically disposed fibers along the length of the member. This is accomplished with a unique apparatus that controls the relative axial and rotational movement between a winding head, which dispensed the filament, and the mandrel. This invention is particularly useful in applying filament to a tapered mandrel to make a tapered pole.
Since one of the major problems with composite poles is the cost, it is particularly desirable to minimize the amount of fiberglass component. It is common to make tapered poles with a base having a larger diameter than the tip. When a tapered pole is made by applying windings from base to tip to provide layers of fiber reinforced resin on a tapered mandrel, the resulting pole tends to have a thicker wall at the basis. This is the opposite of what would be desired based on the strength requirement for a pole and results in loss of some of the economies of tapered poles. U.S. Pat. No. 5,492,579 to Hosford, which is hereby incorporated herein in its entirety by reference, disclosed a computer modeled pole in which the layers do not extend the entire length of the pole, thus allowing a pole with longitudinal zones, having thicker walls at the base, thin walls at the tip and intermediate wall thickness between the base and the tip, and approximate minimum weight for a pole of a given strength. Filament winding is a preferred method of making circular cross section poles.
The second class of processes for making composite poles is pultrusion. Pultrusion refers to a continuous process for manufacturing composites with a constant cross-sectional shape. The process consists of pulling a fiber reinforcing material through a resin impregnation bath and into a shaping die where the resin is subsequently cured. The fiber reinforcing Heating to both gel and cure the resin is sometimes accomplished entirely within the die length, which can be on the order of 76 cm (30 inches) long. In other variations of the process, preheating of the resin-wet reinforcement is accomplished by dielectric energy prior to entry into the die, or heating may be continued in an oven after emergence from the die. U.S. Pat. No. 4,803,819, to Kelsey, which is hereby incorporated herein by reference, discloses use of pultrusion to make hollow composite utility poles having diametrical reinforcing struts which add strength to the hollow pole. Pultrusion may pull strands, rovings (a collection of parallel strands which are not twisted together), spun roving (a collection of teisted or braided strands), or mats (randomly oriented chopped filaments or swirled filaments with a binder cut to the contour of a mold). Pultrusion may produce a tube which is unsupported and merely sawed into lengths after hardening. Alternatively the form may be shaped around a mandrel. Pultrusion is a preferred way of making non-circular cross section poles.
Pulwell Industries (Zhongshan Pulwell Composites Co; Ltd) has a variation known as pullwinding which combines the pultrusion and filament winding methods, by pulling a longitudinal composite layer onto a mandrel followed by applying helically wound layers by filament winding. This approach supplies a tube with high crush strength as well as the stiffness of pultruded poles.
It is known in the prior art, that the use of a core material sandwiched between composite layers can reduce the cost and add strength to a laminated structure. In U.S. Pat. No. 4,682,747 to King, an insulted cross arm for supporting wires on a utility pole is disclosed, comprising an outer shell of polyester resin and a inner core of polyurethane foam. Also in U.S. Pat. No. 5,513,477 to Farber discloses a composite, tapered poles made in segments which are assembled to make a hollow, tapered pole when assembled. In one of Farber's preferred embodiments the segments are made of an outer skin and an inner skin of fiber reinforced resin with a foam block “core” bonded between them in the annual space between the outer skin and the inner skin. The word “core” in this context refers to the central layer of a laminate to which the outer layers of the laminate are attached.
While composite poles have many valuable uses, there is a need for improvement in several areas.
There is a need for less expensive composite poles. There is a need for less expensive composite poles by reducing the wall thickness of the poles. There is a need for improved and simplified methods of construction of composite poles.
There is a need for composite poles with greater strength that is not simply accomplished by thicker walls.
Composite poles made by existing processes of filament winding and pultrusion are by their very nature hollow poles (allowing for internal struts as described above in Farber). The original use was as a substitute for wooden utility distribution poles. In this application, the function of the original wooden pole can be mimicked without routing conduit or other vessels through the pole. However, in other applications the interior of the pole is very important. For example, light poles, power poles (e.g. poles for connecting to underground wires), and antennas, all have internal wires which could be provided for in the pole. Also, other mixed use poles could be used to route power lines, data lines, optical lines, and process lines such as lube oil or coolant. There is a need for composite poles having internal provision for routing wires, conduit, process lines and the like.